The present application relates to a memory element that includes a memory layer that stores the magnetization state of a ferromagnetic layer as information and a magnetization-fixed layer in which a magnetization direction is fixed, and that changes the magnetization direction of the memory layer by flowing a current, and a memory device having the memory element.
In an information device such as a computer, a highly dense DRAM that operates at a high speed has been widely used as a random access memory.
However, the DRAM is a volatile memory in which information is erased when power is turned off, such that a non-volatile memory in which the information is not erased is desirable.
In addition, as a candidate for the non-volatile memory, a magnetic random access memory (MRAM) in which the information is recorded by magnetization of a magnetic material has attracted attention and therefore has been developed.
The MRAM makes a current flow to two kinds of address interconnects (a word line and a bit line) that are substantially perpendicular to each other, respectively, and inverts the magnetization of a magnetic layer of a magnetic memory element, which is located at an intersection of the address interconnects, of the memory device by using a current magnetic field generated from each of the address interconnects, and thereby performs the recording of information.
A schematic diagram (perspective view) of a general MRAM is shown in FIG. 9.
A drain region 108, a source region 107, and a gate electrode 101, which make up a selection transistor that selects each memory cell, are formed at portions separated by an element separation layer 102 of a semiconductor substrate 110 such as a silicon substrate, respectively.
In addition, a word line 105 extending in the front-back direction in the drawing are provided at an upper side of the gate electrode 101.
The drain region 108 is formed commonly to left and right selection transistors in the drawing, and an interconnect 109 is connected to the drain region 108.
In addition, magnetic memory elements 103, each having a memory layer whose magnetization direction is inverted, are disposed between the word line 105 and bit lines 106 that are disposed at an upper side in relation to the word line 105 and extend in the left-right direction. These magnetic memory elements 103 are configured, for example, by a magnetic tunnel junction element (MTJ element).
In addition, the magnetic memory elements 103 are electrically connected to the source region 107 through a horizontal bypass line 111 and a vertical contact layer 104.
When a current is made to flow to the word line 105 and the bit lines 106, a current magnetic field is applied to the magnetic memory element 103 and thereby the magnetization direction of the memory layer of the magnetic memory element 103 is inverted, and therefore it is possible to perform the recording of information.
In addition, in regard to a magnetic memory such as the MRAM, it is necessary for the magnetic layer (memory layer) in which the information is recorded to have a constant coercive force in order to stably retain the recorded information.
On the other hand, it is necessary to make a certain amount of current flow to the address interconnect to order to rewrite the recorded information.
However, along with miniaturization of the element making up the MRAM, the address interconnect becomes thin, such that it is difficult to flow a sufficient current.
Therefore, as a configuration capable of realizing the magnetization inversion with a relatively small current, a memory having a configuration using a magnetization inversion by spin injection has attracted attention (for example, refer to Japanese Unexamined Patent Application Publication Nos. 2003-17782 and 2008-227388, and a specification of U.S. Pat. No. 6,256,223, PHYs. Rev. B, 54.9353 (1996), and J. Magn. Mat., 159, L1 (1996).
Magnetization inversion by the spin injection means that a spin polarized electron after passing through a magnetic material is injected to the other magnetic material, and thereby magnetization inversion is caused in the other magnetic material.
For example, when a current is made to flow to a giant magnetoresistive effect element (GMR element) or a magnetic tunnel junction element (MTJ element) in a direction perpendicular to a film face, the magnetization direction of at least a part of the magnetic layer of this element may be inverted.
In addition, magnetization inversion by spin injection has an advantage in that even when the element becomes minute, it is possible realize the magnetization inversion without increasing the current.
A schematic diagram of the memory device having a configuration using magnetization inversion by the above-described spin injection is shown in FIGS. 10 and 11. FIG. 10 shows a perspective view, and FIG. 11 shows a cross-sectional view.
A drain region 58, a source region 57, and a gate electrode 51 that make up a selection transistor for the selection of each memory cell are formed, respectively, in a semiconductor substrate 60 such as a silicon substrate at portions isolated by an element isolation layer 52. Among them, the gate electrode 51 also functions as a word line extending in the front-back direction in FIG. 10.
The drain region 58 is formed commonly to left and right selection transistors in FIG. 10, and an interconnect 59 is connected to the drain region 58.
A memory element 53 having a memory layer in which a magnetization direction is inverted by spin injection is disposed between the source region 57 and bit lines 56 that are disposed in an upper side of the source region 57 and extend in the left-right direction in FIG. 10.
This memory element 53 is configured by, for example, a magnetic tunnel junction element (MTJ element). The memory element 53 has two magnetic layers 61 and 62. In the two magnetic layers 61 and 62, one side magnetic layer is set as a magnetization-fixed layer in which the magnetization direction is fixed, and the other side magnetic layer is set as a magnetization-free layer in which that magnetization direction varies, that is, a memory layer.
In addition, the memory element 53 is connected to each bit line 56 and the source region 57 through the upper and lower contact layers 54, respectively. In this manner, when a current is made to flow to the memory element 53, the magnetization direction of the memory layer may be inverted by spin injection.
In the case of the memory device having a configuration using magnetic inversion by this spin injection, it is possible to make the structure of the device simple compared to the general MRAM shown in FIG. 9, and therefore it has a characteristic in that high densification becomes possible.
In addition, when magnetization inversion by spin injection is used, there is an advantage in that even as miniaturization of the element proceeds, the write current is not increased, compared to the general MRAM performing magnetization inversion by an external magnetic field.